The CO2 generated by the user of the device and exhaled into the breathing circuit line must be absorbed in breathing circuit devices before the breathing gas is fed again to the user of the device. This is brought about by CO2 absorbers in the breathing circuit line, which contain, in general, breathing lime or alkali. Moisture and heat (exothermal chemical reaction of the CO2 with the absorber material) are formed in the CO2 absorber due to the chemical reaction with the CO2. This leads to a corresponding heating and humidification of the air to be inhaled again by the user of the device. The breathing air thus heated and humidified means a physiologically poorly tolerable breathing climate. Various methods have been developed in the state of the art to cool and dehumidify the breathing gas after the CO2 absorber.
Ice is used for cooling in breathing circuit devices commonly used currently. This is complicated in respect to handling, because a block of ice must first be formed and then removed from the freezer shortly before the use of the breathing circuit device and inserted into the breathing circuit device. In addition, it is necessary for this to open the device.
As an alternative to the cooling by ice, a so-called regenerative cooler is also used for the commercially available breathing circuit devices, which uses instead of ice a latent heat storage medium, which makes the melting energy available for cooling. This concept is considerably simpler in terms of handling, because the cooler can be reused time and time again and is stored ready to use in the device. However, the cooling capacity is markedly lower because the PCM (phased change material) has a lower specific cooling capacity at equal volume and it is not possible to reach lower breathing gas temperatures due to the fact that the melting point of the PCM is above room temperature. Examples of such cooled breathing circuit devices are described in DE 879 651 and DE 928 690.
So-called zeolite coolers, which extract heat from the surrounding area by evaporating water and absorb the moisture in a zeolite, are known as another alternative for cooling in breathing circuit devices. Such a cooling means for cooling breathing gas in a breathing circuit device is known from DE 40 29 084 A1. However, the manufacture of such a reusable zeolite cooler is technically very complicated, because the zeolite must be stored under vacuum and tightness must be ensured for a very long time. In addition, the reusable cooler must be regenerated in a complicated manner. The zeolite must be dehumidified for this at temperatures above 200° C. and the water must be condensed in the evaporator. This is not practicable for use in respirators.
Further, zeolite coolers in a deformable packaging are known, which are deformable as cooling elements such that they can come into contact with the breathing circuit line after the CO2 absorber in good heat-conducting contact, as is described in EP 2 374 509 A1. These may be manufactured, in principle, as disposable coolers, so that a complicated regeneration is avoided. However, this leads to a very high cost of use.